1. Field of the Invention
This invention resides in the field of external fixators, which are medical devices that serve as splints to treat fractures of long bones in general and specifically the forearm and distal radius.
2. Description of the Prior Art
Colles' fractures are a common injury among adults, including middle-aged to elderly women who suffer from osteoporosis as well as younger adults who suffer falls during sports or other vigorous activities. A Colles' fracture is a fracture of the radius, i.e., the forearm bone on the thumb side. The fracture typically occurs when one begins to fall and extends one's hand as a reflex to lessen the force of hitting the ground. The fall produces a sudden impact of the body weight on the heel of the hand which results in a fracture of the radius just above the wrist joint with or without an associated wrist joint injury.
The realignment and setting of bones crushed by a Colles' fracture are typically performed with the aid of an external fixator or fixation device, which is a mechanically adjustable splint that is mounted externally to the forearm and hand through percutaneous pins or screws that secure the device to the bones on either side of the fracture site. External fixators are designed to permit initial alignment of the fracture fragments and then stabilize the fragments and injured soft tissue as they heal.
Alignment of the bone fragments is a complex task in view of the numerous degrees of freedom in the region of the forearm, wrist and hand. The typical fracture causes misalignment of the fragments both rotationally and translationally with respect to a conventional set of orthogonal anatomical axes of the forearm, wrist and hand. Translational misalignment can occur for example in the radial-ulnar, palmar-dorsal, and proximal-distal directions, while rotational misalignment can occur about the longitudinal axis of the radius. All of these misalignments must be corrected before the final securement of the fixator. The optimal fixator would be one that contains and effectively integrates all the degrees of freedom necessary to achieve accurate translational and rotational alignment of the fracture efficiently. This is difficult to achieve—the typical fixator of the prior art is incapable of effectively integrating all of these degrees of freedom.
Theoretically, proper alignment of the fracture about the longitudinal axis of the radius could be achieved by proper placement of the fixation pins in the bone. Thus, with a distal set of pins in the stable (index and long finger) metacarpals, a proximal set in the radius at a site proximal to the fracture, and both sets mounted to a fixator, alignment might be achievable when a distraction force is applied between the distal and proximal pins if the pins were inserted in the correct orientation within the plane defined by the stable metacarpals. Achieving this desired orientation of the distal pins is relatively easy, but proper orientation of the proximal pins is considerably more difficult. Numerous fixators and fixator features have been designed to address this difficulty. Even if rotational alignment is achieved, the remaining degrees of freedom used for translational alignment of the fracture are no longer referenced to the conventional set of orthogonal anatomical axes of the forearm, wrist and hand (i.e., those axes that are recognized as a frame of reference among surgeons who specialize in these fractures). Consequently, when adjustments are made to align the fracture translationally, the procedure suffers from three disadvantages. First, translation of the fracture fragments has not been achieved along the conventional anatomical axes. Second, adjustment along a single axis cannot be performed without affecting translation of the fracture along the other two axes. Both of these disadvantages make it difficult for the surgeon to correlate adjustments made to the fixator with x-ray images taken after the adjustment. The third disadvantage is that once all adjustments to the fracture have been made, the flexion-extension axis about which the fixator can rotate is fixed relative to the anatomical flexion-extension axis of the wrist joint. If these axes are not substantially colinear, any wrist flexion or extension will cause misalignment of the fracture.
What is therefore needed is a fixator that enables the surgeon to achieve rotational alignment of the fracture along the longitudinal axis of the radius, even when the proximal pins are inserted in an incorrect orientation (i.e., the pins are not all in a common plane when the fracture is rotationally aligned), and still retain the correct reference between the fixator translational degrees of freedom and the orthogonal anatomical axes of the forearm, wrist and hand.